Abstract :
Oestrosis is a worldwide myiasis caused by larvae of the fly Oestrus ovis, which are obligate
parasites of the nasal and sinus cavities of sheep and goats, especially in Mediterranean
countries. The aim of this study was to compare the infection levels and seasonal patterns
of oestrosis in sheep and goats from areas of similar climate and to explore some potential
risk factors associated with this disease in Greece. Of 450 sheep and goat heads examined,
246 (54%) were infected with O. ovis larvae. Goats (76%, 95% CI 68–82) were more commonly
infected than sheep (38%, 95% CI 37–49). Larval stages were recovered during all months
of the year from both host species, with an overall mean infection intensity of 8.7±13.1
(mean±SD). Host species, month, area and age, but not nose colour, affected the chance of
being infected. Parasite intensity varied but was not affected by these factors except for age
and season. Seasonal variation in prevalence was much more pronounced for larval stage
1, than for total larvae. In sheep, infection was generally more common and intense in early
spring and in autumn, whereas prevalence peaked in goats in winter. Both prevalence and
larval intensity increased with age above 3–4 years in sheep, but not in goats. Patterns of
aggregation were consistent with density-dependent constraints to development in the
host, and suggested lower susceptibility to larval establishment in goats in spite of higher
overall prevalence.
